Pebble heater system and method of operation



Nov. 14, 1950 L. J. WEBER PEBBLE HEATER SYSTEM AND METHOD OF OPERATION 2 Sheets-Sheet 1 Filed Dec. 9, 1946 KOP MJM M T C NR G 6% U w% E NB D T U LI 0 M H 2 O R 30 5 6 AA l HW EEHZ P 23 7EH 4 1 PE a 2 2:2

COMBUS I GAS OR FUEL . 4 wa 2R ATTORNEYS Nov. 14, 1950 L. J. WEBER 2,530,274

PEBBLE HEATER SYSTEM AND METHOD OF OPERATION Filed Dec. 9, 1946 Sheets-Sheet 2 PEBBLES FROM ELEVATOR COOLER PEBBLE FROM ELEVATOR.

PEBBLE HEATING CHAMBER REACTOR COOLER PEBBLES ELEVATOR HOTTER PEBBLES TO ELEVATOR INVENTOR L. J. WEBER ATTORNEYS Patented Nov. 14, 1950 PEBBLE HEATER SYSTEM AND METHODOF OPERATION LouisJ'. Weber, Bartlesville, Okla, assignor to PhillipsPetroleum Company, acorporation of Delaware Application December 9, 1946', Serial'N0l,715,076.

( 01,,23ee28 l.)

ISClaims. 1

This. invention relates toimproved pebble heater.v apparatus and to, an improvedzprocess for treatinggases. in apebble heater, A specific as-. pect. of the invention. pertains to a method and apparatus forrecirculating separate streamsof pebbles: at different, temperatures from various points in the main pebble streambelow the heatingachamber tothe pebble heating chamber of a pebbleheater unit.v

Typical pebble heater operation involves heating a. mass. of small refractoryelements called pebbles in a slowly descending stream by countercurrentcontact with hot, gas, such as combustion gas; in an-upper chamber, passing the resulting hot massof pebbles through a lower'reactiona or treating chamber .invcontact with a gas to be treated. or converted. As the pebbles leave the reaction chamber they descendv into. an elevator which liftsthem to aheightabove the inlet tothe pebble heating chamber from which they descend into the pebble heating chamber to. be again ree heated and passed-through the reaction chamber. The flow of gases through the two chambers may-be concurrent as well as countercurrent.

The term pebble as used throughout the specification denotes any flow-able material in particulate form which withstands the extremely-high temperatures involved without serious disintegration. Various refractory materials in the form of small spheres of a size of about V inch to about l inch in diameter, more practically, inch'to"% inch in diameter function advantageously. Pebbles of uniform size and shape are preferable but 'they'may be irregular in-both size and shape. Since the pebble heater has its eat t u i yi eati an /qr eacfiirn l es t mnera u e ot 'frqmlabcut 13 ab ut 30 .0 E peb e .materialsmust selec ed which areextremcly ru ed at. these h h empe ature Pebblesmaybe relatively inert toward theea cs being treatedor may behighly catalytic. Such materials as alumina .beryllia, zirconia, .mullite, Periclase, siliconv carbide; clays,.and, synthetic metalox d ae s ake ex el ent con ac -mater ls forsomeprocesses. jlfhesemateri 4 y pregnated withtrnore highlyactivevcatalyti ma e a Pe le or metal and v carbon may .al qibe e Thi -inven i n i applicabl toe-an as.-.Qlid c ntac ,onc ati n whioh; a r ed-9 levated temperatures. One of the principal applications is.in: the -conversion: of ihyd carbons nvolvi thermalandforicatalytic processes. Theiinventiomislalso applicablatc theheating ot feiedair.

steam, andother gasesin which little or. notifie e ion s. n ves It-isan object of the present invention to pro; vide a. meansv and; method of; obtaining increased therm l efiiciency, in pebble heater operation; It. s: a so b ct 9 h ent o to P ovid c m i-" flexbl bnera m i: a P e he te uni A ur er ob ect s i red e h rma a k to pebbles in; ebble heater operation with conseue redue pn in p l br ka t 'er' jects of the; invention will-become apparent from he ac qm n me dialo u M in eni o P ovid a m d an m enw withd n m t streams of b le fat li eren empe e ur sfr m P e heater emh -he v the eat i l and r t d c g h individual pebble stream into the pebble heating chamb r- The bette Peb l S r am w th drawnfromany desired level within the pebble chamber above thelevel from which the cooler pebble stream is withdrawn. Whileit i p -e.- ferred to reintroduce thevarious pebble streams at difierent temperatures into the pebble heating chamber atdifierent levels according to. the item; perature of. the-streamv being introduced order ta introducethehot pebbles at a point ofsube fi l l y the same emp atur W Pe hems es he a -3 .4 pebble t ea may b ntroduced at about the same point andat about the same. level. In pebble heater installations ut izin t lcb m l pl t m atlliiere-nt temperatures are withdrawn f rom the re action or gas treating chamber and reintroduced into the pebbleheating chamber, preferabli at temperaturelevels according tothe temperature of the. individual stream. Some Dflbble heater? in;- stallations utilize a third chamber positioned below the reaction chamberin which the pebble stream transfers heat to the feedgas being treat-.- ed in the reaction chamber. In this type o f installation, the cooler pebble stream is withdrawn from the bottomof the lower chamber or gas preheating chamber, but hotter streams of pebbles mayt e i w-n rom a high level n the lower chamber, from the throat connecting the reaction a b r a d the o e mbe o irqm any desired levelinside the reaction chamber.

Other pebble heater installations utilize a fourth chamber positioned above the pebble heater chamber proper and termeda pebblepreheating chamber. In this fourth chamber pebbles are preheated by contact with such gases as the product. gas, the flue gas. from the pebble heating chamber proper, or any other Waste heat. gas. Inan installation utilizing a pebble preheating chamber the coldest stream is introduced to the upper portion of pebble preheating chamber, but hotter streams may be introduced to the pebble heating chamber proper, or to the pebble preheating chamber at various levels. For instance, it is feasible to introduce the coolest pebble stream into the top of the pebble preheating chamber, a hotter stream to a lower level in the pebble preheating chamber and the hottest pebble stream to a desirable level in the pebble heating chamber proper. When only two streams of two different temperatures are withdrawn from the system, the hotter stream may be introduced advantageously at any desirable level in either the pebble preheating chamber or the pebble heating chamber depending upon the temperature of the hotter pebble stream and the temperatures obtained in the two chambers.

My invention improves thermal eficiency in pebble heater operation. In endothermic proc esses in which gases fed into the lower section of the reaction chamber are preheated a considerable amount before reaching the reaction temperature, most of the reaction, and therefore most of the heat transfer between pebbles and gas occurs in the upper portion of the reaction chamber. This means that in situations where the whole pebble stream is contacted with the feed gas in the lower half of the chamber, the outlet temperature of the pebble stream is not sufficiently low to utilize to the greatest extent the heat in the combustion gas in the pebble heating chamber. .It is quite obvious that the gas passing through the pebble heating chamber cannot be reduced in temperature below the temperature of the incoming pebbles. My invention makes it possible to reduce the outlet temperature of the main pebble stream to such an extent that greater utility is made of the sensible heat in the combustion gas in the pebble heating chamber. This is made possible by removing any desirable portion of the pebble stream passing through the reaction chamber from a high temperature level therein and reintroducing the hotter pebble stream into the pebble heater chamber at a comparable temperature point thereby effecting greater reduction in the temperature of the remaining descending pebble stream and consequent lower stack gas temperature. In order to facilitate understanding of the invention, reference is made to the drawing of which Figure l is an elevational view partly in section of one arrangement of apparatus according to the invention. Figure2 is a fragmentary sectional view on a vertical plane illustrating one modification of the pebble inlet means to the pebble heating chamber. Figure 3 is a fragmentary sectional view on a vertical plane illustrating one modificationof means for withdrawing separate streams of pebbles from a pebble heater unit.

Referring in detail to Figure 1, numeral I6 designates a pebble heating chamber having a metal shell H and a refractory insulating lining 12. Numeral l3 refers to an inlet for hot combustion gas or fuel to be burned in zone as surrounding refractory arch support l8, having holes 19 therein for passage of hot combustion gas therethrough. Numeral l4 designates the stack for removal of flue gas. Pebble inlets I5 and It admit cooler and hotter pebble streams respectively. A removable section ll on the lower end of pebble inlet It provides for regulating the level at which pebbles are introduced into the interior of the heating chamber. End section or member I! may be attached to pebble inlet conduit [6 in any desirable manner other than that shown, such as a threaded joint or a slip joint. Heating chamber 10 encloses a slowly descending mass of pebbles having a top surface 2| and forming a vapor collecting space 22 above the bed of pebbles.

Pebble heating chamber [0 is connected to reaction chamber 25 by a refractory-lined throat 24. Chamber 25 which is used as a reaction chamber or gas heating chamber has a metal shell 26 and a refractory lining 2?. Numeral 28 refers to an inlet for admitting feed gas to annular space 34 surrounding the conical bottom 32, which is perforated by holes 33 for passage of the feed gas into the reaction chamber. Numeral 29 designates a product take-off line. The pebbles passing into the lower chamber through throat 24 form a pebble bed having a top surface as and providing a vapor space 23 between the bed of pebbles and the dome of the treating chamber. Pebble outlets 3i and 35 are arranged concentrically with each other for the removal of a cooler and a hotter pebble stream, respectively. Outlet conduit 35 terminates in its upper end in a removable section 36 which provides for withdrawal of pebbles from any desired level in chamber 25. Conical bottom 32 is supported in the reaction chamber by ring 40 which is welded to shell 23. Pebble outlet 3! is in closed communication with chute 4i, pebble elevator 42, and chute 43 for circulation of a stream of pebbles back to pebble heating chamber lil via pebble inlet !5. Pebble outlet 35 is in closed communication with chute 3?, pebble elevator 38, and chute 39 for return of a hotter stream of pebbles to pebble heater 10 via pebble inlet I6.

Figure 2 shows a modification of the means for admitting pebbles to the pebble heating chamber of Figure 1. (Similar parts in Figures 1,. 2, and 3 are numbered alike.) Pebble inlet conduit [6 extending into heating chamber W is in slidable relation with pebble inlet i5, through adjustable packing gland 45 positioned on the upper end of conduit 64, which is fastened securely to the end member of pebble inlet conduit 15. A set screw 46 aids in securing pebble inlet conduit IS in any desirable elevation adjustment.

Figure 3 shows a modification of the means for withdrawing two separate streams of pebbles from reaction chamber 25 of Figure 1. Pebble outlet conduit 35 forms a slip joint with conduit 41 and may be adjusted vertically for different levels of pebble takeoff in reaction chamber 25. A screw or bolt 58 serves to tighten slip-on conduit 4'! and thus secure conduit 35 at any desirable elevation.

It is imperative that pebble heater apparatus be designed so as to permit relatively free flow of pebbles through the various pebble passageways. Where pebble passageways of circular cross section are utilized it is found that the diameter thereof must be 6 or more pebble diameters. This means that conduits 35 and I6 must have a minimum diameter of 6 pebble diameters. It is also found that the annular passageways in conduits l5 and 3| must be at least 3 pebble diameters across. Since a blocking gas, such as steam, is usually admitted to the various pebble passageways to prevent escape of gases to the pebble chambers there is a practical limit on the maximum dimensions of these various pebble passageways.

Pebble heater apparatus is applicable to a variety of processes ranging in temperature from about 1300 to 3000 F. The materials used in the 4 a'esig'nur Figure- 1 provides for. flexibility of ration-byvarying'the length of theextension attached to the pebbleinlet and .:pebble.- outlet condenser the hotter pebble stream. The in'odifioation illustrated in'Fig'ure 2 makes i-tzpos- Sibl t'o'iiafy the p'i' itit of inlet without shiifiting sewn operation. It inay also be desirable to use this inodificetion for a pebble outlet in thef s'ame installation; Ifuesrred, the upper end of pebble outlet 35, or extension member 36, may' be To illustrate the invention 'in a hydrocarbon cracking process, the mass =of pebbles slowly d'eseem n "through pebble heater chamber is heated 'by contact with hot combustion-'Tgas adiiiitted th-rough line1-3-, passing upwardly through hol'es I 9; a'n dout through stack -l'4. The pe'bbles pa'ss'in'gthroug'h throat 24 are at-a temperature ii-bowie a predetermined reaction temperature and as they" pass through reaction chamber 25, they are-conta-cited'by a stream of suitable hydroearfbdn's admitted through line -28 and passing throughhdle 3'3 intof'the pebble bed. The lower half of *the reaction chamber "serves as "a hydrocarbon'preheating chamber, since most of the craejki'ngtakespiacezin the'up'p'er portion of the i'ieaetion'eh'amber. It is "there that the greatest amount, of heat-trainer er between the pebbles and the gas tali's'plaee. It'is preferable to remove thefiiotten stream o fpebbles from near the fringe of the cracking zone, thiis permittingthe remaining n iass -of-pebbles to:preheat "the feed gas and becooled to alower degree than they would otherwise; Efiluents from the reaction zone pass out through line 29 and are led to any desirable gas 7 separation or=-other treatment-meansnot shown.

The colder mass of pebbles exitthroughoutlet 3| into chute 4|, which takes them into ;a bucket or other type "elevator '42. Elevator "42 is operatedbya: variable speed motor not show-n whichzcontrols the rateat which pebbles arerecirculated in the cooler stream. The-cooler strea'zm'of pebbles flows through chute 4'3rinto inlet 11-5 and again-"enters the "pebble heating chamber. The'hotterfstreamf of pebbles withdraiwmthrough outlet flows into'chute'31'which takes it toelevator 38'. This elevator which is "als'ooperated by a variable speed motor elevates the pebbles anddrops them into chute 39 from whichthey flow into inlet conduit l6 and are delivered to the heating chamber at a point wliere' the temperature of the main mass of peb- =bles is a pproximatelythat of the-hotter pebble stream-being-ifitroduced thereto.

in a 'ty'p'ical utilization of-my invention, a feed stock having the following composition by' w'eight per cefit:

re -scenes: in: apparatus arr nged accordmg to 'ing chamber.

6 #Ei'gure 1 'tornrodircelianxoleihrerichsgas:iof thez iol lowing'i c'ompos'ition fby weig'ht-zper cent:

Hydrogen 2.1 Methane h 2120 Ethylene 36.5 Ethane V 1334 Pitdpjileh E934 Propane '71:? Butanes and heavier i "919 under the iollo'wing. temperature; conditions:

F. Feed'in line286Figfil) 1'00 Producrinnne 29' 1750 Combustion gas in line 13' 3000 steel; 'gas'in'line M 5.00 Pebbles in throat -24 "2000 Pebble streamfou'tlet 3| roe Pebblefstream ini'in'let "1'5 375 Pebble streaminloutretes' "I560 Pbble'st'reamin'oiitlet l6 D A relatively constant feed1rate= of;68y,623 cu. 5ft. per 'hour is maintained with a production of 4229157 .011. f-t.- -ofiproduct.gas using inch dense smadespossibi'er-by'my invention and th'e stackygas temperature ca-n only approach the temperature of the: pebbles introduced into thetop ofthe heat Theimproved thermal efliciency effected by: myinvention: is obvious. It is also ape -parent -that,=-with-:a'feedigas+pebble exit tempera:- ture difiere'ntialof about 300---F.-as effected by this invention, compared'with'a temperature differential of'about-600 F. between outletpebbles andifeed. gas obtained. by prior art practices, much pebble disintegration due to thermal shock lisavoided by my invention.

Various?- modifications of the. invention will "be-'- com'e-:-iapparent; to I those skilled inzlthe. art. L'Ifhe illustrative details -disclosed:ia're'inet. to'be icon S't'rfied "as ini posing u nnecessar'y limitations upon the invention;

I claim: 7

"LA-pebble heater for'heating-a descending contiguous mass of pebbles comprising a ve'rti 'cally elongated cylindrical closed vessel; a "gas pervious refractory partitiondefining incooperation'With t-he walls-andbottom closure member ofsaid vessel a combustion chamber in the" lower portion thereof; apeb'blepassageway com-municating' between an" axially disposed opening in said partition and the pebble outlet hereinafter named; means for introducing a combustiblemix Qture to" said combustion chamberya gas outlet in the-upper 'portionof s'aid'vessel; a pebble outlet substantially axiallypositioned in the bottom-"6f said vessel; means for introducing two "separate streams of 'pebbles *(one a-"relatively hotter and the other a relatively cooler pebble stream) "into the upper portion of said vessel, said means'com prising'afpair (if-concentric conduits of sufiicient diameter difierent'ia-l toform an annulus between thefinner and'outer conduits ofsaid pair of su'flic'ient 1 cross section to permit relatively freeflow -of-'="pebb'le's'-therethrough, said inner conduit ad; justably extending into said vessela subsjtantiel distance for delivery of said hotter pebble stream and said outer conduit extending thereinto a lesser. distance for delivery of said cooler pebble stream.

2. The apparatus of claim 1 further characterized in that said inner conduit extends outwardly from said vessel a greater distance than said oute'r'conduit'and is fixed in slidable relation therewith. i

' 3. The apparatus of claim 1 further characterized in thatsaid inner conduit is in fixed relation with said outer conduit and terminates in its lower end in a removably attached section adapt-.- ed for varying the depth of extension of said inner conduit into said vessel.

4. Pebble heater apparatus for heating a descending contiguous mass'of pebbles comprising a vertically elongated. cylindrical vessel having top and bottom closure members; a pebble outlet substantially axially positioned in said bottom; a. gas-pervious refractory partition in the lower portion ofsaid vessel disposed in spaced-apart relation to the bottom'closure member thereofso as to form a combustion chamber therebetween; a refractory-walled pebble passageway communicating between an axially disposed opening in said partition and said pebble outlet; means for introducing a combustible mixture to said combustion chamber; a gasoutlet means in the upper portion of said vessel; means for introducing a relatively cool stream of pebbles through the top of said vessel comprising a conduit opening into said vessel, said conduit being closed on the upper end and in communication with a pebble supply chute; and means for introducing a relatively hot pebble stream into said vessel through the closed upper end of said first-named conduit means, said means comprising a conduit of substantially smaller cross section than said first-named conduit means extending interiorly of said firstnamed conduit means into said vessel a substantial distance, being adapted to introduce said hot pebble stream into said vessel at a point substantially below the top of said vessel, and forming 'a pebble fiow path with said first-named conduit means for said relatively cool pebble stream.

5. The apparatus of claim 4 further characterized in that said inner conduit is in fixed relation with said outer conduit and terminates in its lower end in a removably attached section adapted for varying the depth of extension of said inner conduit into said vessel.

6. Pebble heater apparatus for heating a descending contiguous mass of pebbles comprising a vertically elongated cylindrical vessel having top and bottom closure members; supply and discharge means leading to and from said vessel for flowing a hot gas therethrough; a pebble outlet substantially axially positioned in said bottom; means for introducing a relatively cool stream of pebbles through the top of said vessel comprising a conduit opening into said vessel, said conduit being closed on the upper end and in communication with a pebble supply chute; and conduit means positioned concentrically with said firstnamed conduit means, of lesser diameter than said first-named means, slidably adjustable in a vertical direction therewith, and extending into the interior of said vessel, said means being adapted to introduce a relatively hot stream of pebbles into the interior of said vessel to varying depths, said conduit means forming an annulus along a portion of its length with said first-named conduit means for now of said cool pebble stream therethrough, l

'7. Pebble heater apparatus comprising an upper closed vessel having gas inlet and outlet means adapted for passing a hot gas through said vessel; pebble inlet conduit means for introducing two separate streams of pebbles at different temperatures to the upper portion of said vessel; pebble outlet means in the lower portion of said vessel; a lower closed vessel having gasinlet and outlet means adapted for passing gases to be treated through said lower vessel; pebble inlet means in the upper portion of said lower vessel in communication with said pebble outlet means in said upper vessel; conduit means for withdrawing two separate streams of pebbles at different levels and at different temperatures through the lower portion of said lower vessel; and means for transferring said separate pebble streams to the pebble inlet conduit means corresponding in temperature in said upper vessel.

8. Pebble heater apparatus comprising an upper closed vessel having gas supply means in the lower portion and gas discharge means in the upper portion; a first pebble inlet conduit means adjustably extending into the upper portion of said upper vessel for introducing a relatively cool pebble stream into the upper portion of said upper vessel; a second pebble inlet conduit means for introducing a hotter pebble stream into the upper portion of said upper vessel; pebble outlet means in the lower portion of said upper vessel; a lower closed vessel having gas supply means in the lower portion and gas discharge means in the upper portion; pebble inlet means in the upper portion of said lower vessel; conduit means connecting said pebble outlet means in said upper vessel with said pebble inlet means in said lower vessel for flow of pebbles therebetween; conduit means for withdrawing a, relatively cool pebble stream from the lower portion of said lower vessel; pebble elevator means in communication with said last-named means and with said first pebble inletmeans in said upper vessel; a second pebble outlet conduit means adjustably extending into the lower portion of said lower vessel for withdrawing a hotter pebble stream from a higher level in said lower vessel; and pebble elevator means in communication with said last-named means and with said second pebble inlet means in said upper vessel.

'9. Apparatus of claim 8 further characterized in that said second pebble inlet means extends into said upper vessel a substantial distance and is fixedin slidable relation with a top member thereof to vary the depth of extension, and further in that said second pebble outlet means in said lower vessel is fixed in slidable relation with a bottom member thereof to vary the level at which pebbles are withdrawn therefrom.

10. Apparatus of claim 8 further characterized in that said second pebble inlet means is equipped with a removable lower end section adapted to vary the level in said upper vessel at which pebbles are introduced thereto, and further in that said second pebble outlet means is equipped with a removable upper-end section adapted to vary the level in said lower vessel at which pebbles are removed therefrom.

11. Pebble heater apparatus for eifecting heat exchange between a gravitating mass of hot pebbles and a cooler gas stream which comprises a vertically elongated closed vessel having a pebble inlet in the upper portion and a pebble outlet axially positioned in the bottom thereof; a gaspervious, funnel-shaped member extending across the lower portion of said vessel so asto funnel pebbles into said pebble outlet and provide an annular gas space between said member and the bottom of said vessel; means for introducing gas to said gas space; means for withdrawing gas from the upper portion of said vessel; a pebble conduit adjustably extending upwardly into the interior of said vessel through said funnel-shaped member so as to provide a means for withdrawing a stream of pebbles hotter than the pebbles fiowing out through the outlet of said funnel.

12. Pebble heater apparatus for efiecting heat exchange between a gravitating mass'of hot pebbles and a cooler gas stream which comprises a vertically elongated closed vessel having a pebble inlet in the upper portion and a pebble outlet axially positioned in the bottom thereof; a gaspervious, funnel-shaped member extending across the lower portion of said vessel so as to funnel pebbles into said pebble outlet and provide an annular gas space between said member and the bottom of said vessel; means for introducing gas to said gas space; means for withdrawing gas from the upper portion of said vessel; 9, first pebble conduit in communication with said pebble outlet; a second inner pebble conduit of smaller cross-section than said first pebble conduit extending interiorly thereto into the interior of said vessel so as to effect the withdrawal of separate streams of pebbles at difierent temperatures from said vessel through each conduit.

13. Apparatus of claim 12 further characterized in that said inner conduit is attached to said outer conduit in slidable relation therewith and adapted to remove pebbles from varying levels inside said vessel.

14. Apparatus of claim 12 further characterized in that said inner conduit is in fixed relation with said outer conduit and terminates in its upper end in a removably attached section adapted for varying the level at which pebbles are removed by said inner conduit.

15. Pebble heater apparatus comprising an upper closed vessel having a gas-pervious partition intermediate its top and bottom thereby dividing said vessel into a pebble heating chamber above and a combustion chamber below said partition; pebble outlet means in the lower portion of said vessel; a refractory-walled pebble passageway connecting said pebble outlet means with said pebble heating chamber through an opening in said partition; means for introducing a combustible mixture to said combustion chamber; means for withdrawing flue gas from said pebble heating chamber; a first pebble inlet conduit in communication with the upper portion of said pebble heating chamber for introducing a relatively cool pebble stream thereto; a second pebble inlet conduit in communication with the upper portion of said pebble heating chamber for introducing a hotter pebble stream thereto; a lower closed vessel having pebble inlet means in the upper portion and axially positioned pebble outlet means in the bottom thereof; a gas-pervious, funnel-shaped member extending across the lower portion of said vessel so as to funnel pebbles into said outlet means and provide an annular gas space between said member and the bottom of said vessel; means for introducing gas to said gas space; means for withdrawing gas from the upper portion of said lower vessel; means for passing pebbles from the pebble outlet in said upper vessel to the pebble inlet in said lower vessel; a first pebble outlet conduit in communication with the pebble outlet means in said lower vessel for withdrawing a relatively cool stream of pebbles therefrom; pebble elevator means in communication with said first outlet conduit and with said first inlet conduit; 3, second pebble outlet conduit in the lower portion of said lower vessel for withdrawing a stream of pebbles from a higher level therein than said first conduit; and pebble elevator means in communication with said second outlet conduit and with said second inlet conduit.

LOUIS J. WEBER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number 

1. A PEBBLE HEATER FOR HEATING A DESCENDING CONTIGUOUS MASS OF PEBBLES COMPRISING A VERTICALLY ELONGATED CYLINDRICAL CLOSED VESSEL; A GAS PERVIOUS REFRACTORY PARTITION DEFINING IN COOPERATION WITH THE WALLS AND BOTTOM CLOSURE MEMBER OF SAID VESSEL A COMBUSTION CHEMBER IN THE LOWER PORTION THEREOF; A PEBBLE PASSAGEWAY COMMUNICATING BETWEEN AN AXIALLY DISPOSED OPENING IN SAID PARTITION AND THE PEBBLE OUTLET HEREINAFTER NAMED; MEANS FOR INTRODUCING A COMBUSTIBLE MIXTURE TO SAID COMBUSTION CHAMBER; A GAS OUTLET IN THE UPPER PORTION OF SAID VESSEL; A PEBBLE OUTLET SUBSTANTIALLY AXIALLY POSITIONED IN THE BOTTOM OF SAID VESSEL; MEAND FOR INTRODUCING TWO SEPARATE STREAMS OF PEBBLES (ONE A RELATIVELY HOTTER AND THE OTHER A RELATIVELY COOLER PEBBLE STREAM) INTO THE UPPER PORTION OF SAID VESSEL, SAID MEANS COMPRISING A PAIR OF CONCENTRIC CONDUITS OF SUFFICIENT DIAMETER DIFFERENTIAL TO FORM AN ANNULUS BETWEEN THE INNER AND OUTER CONDUITS OF SAID PAIR OF SUFFICIENT CROSS SECTION TO PERMIT RELATIVELY FREE FLOW OF PEBBLES THERETHROUGH, SAID INNER CONDUIT ADJUSTABLY EXTENDING INTO SAID VESSEL A SUBSTTIAL DISTANCE FOR DELIVERY OF SAID HOTTER PEBBLE STREAM AND SAID OUTER CONDUIT EXTENDING THEREINTO A LESSER DISTANCE FOR DELIVERY OF SAID COOLER PEBBLE STREAM. 